1. Field of the Invention
The present invention relates to a cutter device for a printer for cutting paper after printing.
2. Description of the Related Art
Thermal printers have been widely used as output devices for facsimile machines, POS systems and the like. In many cases, a roll of heat-sensitive paper is used as the recording paper.
Some of these printers use a roll of paper and are equipped with a cutter device for automatically cutting the recording paper after printing into an appropriate length.
The cutter device is equipped with a stationary blade and a movable blade, and the movable blade is driven with a predetermined timing using a dedicated drive source or a printer drive source to cut the recording paper after printing.
The movable blade is of two types: a type in which a round blade rolls along the stationary blade in a direction perpendicular to the recording paper conveying direction; and a so-called guillotine-type in which a plate-like blade with a clearance angle at the end moves toward and away from the stationary blade.
FIG. 6 shows an example of the guillotine type cutter device. FIG. 6 is an exploded perspective view showing an example of the construction of a conventional guillotine type cutter device C2.
As shown in FIG. 6, there are provided five gears arranged on an upper plate 136 of a head support plate 116: a gear (driving gear) 127, and driven gears 128, 129, 130, and 131, and axles 127a, 128a, 129a, 130a, and 131a for rotatably mounting these gears to the upper plate 136. These gears 127, 128, 129, 130, and 131 are arranged two-dimensionally along the upper plate 136 arranged parallel to the paper feeding direction X. Reference numeral 113 indicates a platen roller for conveying the recording paper (not shown) in the X-direction.
In a cutter drive mechanism 120, power transmitted through a bevel gear 126 is transmitted successively by way of the gear (driving gear) 127 and the driven gears 128, 129, 130, 131. The construction of the cutter drive mechanism 120 is such that the gears 128 and 1431 move in synchronism with a gear ration of one-to-one. At positions off the rotation centers of the gears 128 and 131, drive pins 128b and 131b protrude downwardly for driving the movable blade 112, causing a slide plate 117 to slide in the paper feeding direction X. The slide plate 117 has two guide grooves 117a and 117b in the form of elongated round holes extending in the direction perpendicular to the paper feeding direction X. At the time of assembly, the drive pins 128b and 131b are inserted into the guide grooves 117a and 117b under the upper plate 136 fixed to the upper surface of the support plate 136 fixed to the upper surface of the support plate 116 (on the thermal head side) so as to allow movement (sliding) in the paper feeding direction X with the cutter drive mechanism 120 therebetween. Thus, when the gears 127 through 131 rotate, the drive pins 128b and 131b rotate, and, with this rotation, the slide plate 117 reciprocates in a direction parallel to the paper feeding direction X. As a result the movable blade 112 fixed to the slide plate 117 reciprocates between the home position H and the cutting position C. In FIG. 7, the movable blade 112 is at the home position H, and in FIG. 8, it is at the cutting position C.
FIG. 9 shows the construction of the cutter drive mechanism 120.
As shown in FIG. 9, on the gear 128 of the cutter drive mechanism 120, there is formed a clutch portion 141 with a part of its teeth cut away; further, due to an engagement pin 145 provided at a position off the rotation center, the gear 128 is pressurized by a torsion spring 139 in a predetermined direction, which, in this example, is counterclockwise as seen from above the cutter drive mechanism 120.
The gear (driven gear) 128 and the gear (driving gear) 127 form a one-revolution (single-revolution) clutch mechanism 140. In the condition in which the clutch portion 141 is in contact with the gear 127, the gear 128 is pressurized counterclockwise by a force F2, so that, if the gear 127 rotates counterclockwise, there is no gear meshing, and no power is transmitted.
When the gear 127 rotates clockwise, it is engaged with the gear 128, and power is transmitted. And when the gear 127 rotates clockwise and the gear 128 makes one revolution, the movable blade 112 makes one reciprocation between the home position H and the cutting position C. Thereafter, when the gear 127 rotates counterclockwise, the clutch 141 is restored, while in contact with the gear 127, to the angle at which it is pressurized by the spring 139.
Thus, the angle of the gear 128 when printing is being performed through counterclockwise rotation of the gear 127 is always kept at a fixed level, and, during printing, the movable blade 112 is set at the home position H without fail.
By using the one-revolution mechanism 140 thus constructed, it is possible to reliably maintain the movable blade 112 at the home position without using any optical sensor or limit switch, making it advantageously possible to provide a cutter device C2 of a simple construction and high positional accuracy.
In the one-revolution clutch mechanism 140 provided in the cutter drive mechanism 120 of the cutter device C2 shown in FIGS. 6 through 9, when the gear 127 rotates counterclockwise, it idles with its teeth flicking clockwise the edge portion of the cutout portion 141 of the gear 128, so that no power is transmitted to the gear 128, and the cutter device is placed in the printable state in which the movable blade 112 is kept on standby at the home position H. The torsion spring 139 which engages in this state with the engagement pin 145 of the gear 128 to impart an urging force in the direction F2 is relatively large, and its resilient force is strong, so that there is a great crackling noise when the gear 128 is flicked, which constitutes a noise factor in the printer operation.
Further, the vibration when the gear 128 is flicked is relatively great, and the vibration generated between the gear (driving gear) 127 and the gear (driven gear) 128 during printing may be transmitted to the entire printer through the other driven gears 129, 130, 131, etc., thereby adversely affecting the printing quality.
This invention has been made with a view to solving the above-mentioned problems in the prior art. It is an object of this invention to provide a cutter device for a printer in which in a printing state in which a movable blade is on standby for movement, it is possible to reduce a flicking noise generated between gears and to restrain vibrations generated thereby.
In order to achieve the above-mentioned object, according to the present invention, there is provided a cutter device for a printer equipped with a movable blade (17) and a stationary blade (300) for cutting at a predetermined position recording paper which has undergone printing by a printing means, the cutter device including:
a cutter drive mechanism (20) for causing the movable blade to advance and retreat with respect to the stationary blade,
the cutter drive mechanism being equipped with a rotation mechanism which causes, through one rotation of a driven gear (28) connected to the movable blade, the movable blade to make one reciprocation between a home position (H) spaced apart from the stationary blade by a predetermined distance and a cutting position (c) where it cuts the recording paper through cooperation with the stationary blade,
the rotation mechanism being connected to a one-way clutch mechanism (40) connected to a driving means capable of normal and reverse rotation and adapted to rotate a platen roller (13) in the paper feeding direction when the driving means makes normal rotation and to drive the movable blade of the cutter when the driving means makes reverse rotation,
the one-way clutch mechanism being composed of a driving gear (27) connected to the driving means and a driven gear (28) in mesh with the driving gear,
the driven gear having in a part of its outer peripheral portion (101) where teeth (G2) are formed a cutout portion (102) corresponding to a predetermined number of teeth,
the tooth surface of a trigger gear member (T) that is equipped with teeth (G3) in a number less than that corresponding to the cutout portion facing the cutout portion with arranging an arm portion (A) supporting the tooth surface while urging it clockwise,
urging means (torsion spring S) for imparting a clockwise urging force and being arranged on the arm portion of the trigger gear member.
the driven gear being equipped with a rotation regulating means (K) for regulating counterclockwise rotation of the driven gear itself with the movable blade being at rest at the home position,
the driving gear being also engaged with the tooth surface of the trigger gear member to transmit driving force to the driven gear when it rotates counterclockwise and causing the teeth of the trigger gear member to retreat against the urging force so as to flick them counterclockwise when it rotates clockwise so as not to transmit driving force to the driven gear regulated in counterclockwise rotation by the rotation regulating means.
By the foregoing construction, the driven gear is equipped with members such as a relatively small trigger gear member and urging means, so that it is possible to reduce the size of the one-way clutch mechanism as compared with the prior art. Since the urging force of the trigger gear member is small, it is possible, during execution of printing and paper feeding, to reduce the noise made when the driving gear rotates clockwise to flick the teeth of the trigger gear member as compared with the prior art.
Further, since it is also possible to reduce the vibration when the driving gear rotates clockwise to flick the teeth of the trigger gear member, it is possible to avoid a situation in which vibration generated in the one-way clutch mechanism is transmitted to the components of the printer to adversely affect the printing quality.
Since it is accommodated inside a hollow portion formed in the inner periphery of the driven gear, it is possible to further reduce the size of the one-way clutch mechanism.
Further, it is possible for the arm portion of the trigger gear member to be rotatably supported at a position off the rotation axis of the driven gear, whereby it is possible to realize, with a simple construction, a counterclockwise retreating movement of the trigger gear member when the driving gear rotates clockwise.
Further, the arm portion of the trigger gear member is formed of a flexible material. When the driving gear rotates clockwise, the arm itself undergoes counterclockwise deformation, making it possible to cancel its engagement with the teeth of the driving gear. Thus, when the driving gear rotates clockwise, it is possible to aid the counterclockwise retreating movement of the trigger gear member, and to absorb the vibration when the driving gear rotates clockwise to flick the teeth of the trigger gear member, thereby restraining the vibration and reducing the noise generated.
Further, the rotation regulating means is composed of a protrusion formed on the bottom surface of the driven gear and having a vertical surface and an inclined surface, a vertical portion arranged in the vicinity of the rotation axis of the driven gear and adapted to engage with the vertical surface of the protrusion in the state in which the movable blade is at rest at the home position to regulate the counterclockwise rotation of the driven gear, and a rotation regulating member equipped with an arm portion adapted to be displaced along the inclined surface of the protrusion when the driven gear is rotated clockwise. Thus, it is possible, with a simple construction, to regulate the counterclockwise rotation of the driven gear itself in the state in which the movable blade is at rest at the home position.